Molecular interactions of STAC proteins with skeletal muscle dihydropyridine receptor and excitation-contraction coupling

Excitation-contraction coupling (ECC) is the physiological process in which an electrical signal originating from the central nervous system is converted into muscle contraction. In skeletal muscle tissue, the key step in the molecular mechanism of ECC initiated by the muscle action potential is the cooperation between two Ca2+ channels, dihydropyridine receptor (DHPR; voltage-dependent L-type calcium channel) and ryanodine receptor 1 (RyR1). These two channels were originally postulated to communicate with each other via direct mechanical interactions; however, the molecular details of this cooperation have remained ambiguous. Recently, it has been proposed that one or more supporting proteins are in fact required for communication of DHPR with RyR1 during the ECC process. One such protein that is increasingly believed to play a role in this interaction is the SH3 and cysteine-rich domain-containing protein 3 (STAC3), which has been proposed to bind a cytosolic portion of the DHPR alpha(1S) subunit known as the II-III loop. In this work, we present direct evidence for an interaction between a small peptide sequence of the II-III loop and several residues within the SH3 domains of STAC3 as well as the neuronal isoform STAC2. Differences in this interaction between STAC3 and STAC2 suggest that STAC3 possesses distinct biophysical features that are potentially important for its physiological interactions with the II-III loop. Therefore, this work demonstrates an isoform-specific interaction between STAC3 and the II-III loop of DHPR and provides novel insights into a putative molecular mechanism behind this association in the skeletal muscle ECC process.

Automated summary

Excitation-contraction coupling is the process by which an electrical signal is converted into muscle contraction. In this study, the interaction between two calcium channels, dihydropyridine receptor (DHPR) and ryanodine receptor 1 (RyR1), during the excitation-contraction coupling process was investigated. The results showed that the protein STAC3 interacts with a subunit of the DHPR known as the II-III loop, and this interaction differs from the interaction with the neuronal isoform STAC2. These findings provide insights into the molecular mechanism of excitation-contraction coupling in skeletal muscle.